A typical X-ray CT device comprises an X-ray generator and an X-ray detector which are placed opposing each other with a subject therebetween, and realizes CT imaging by executing radiation and detection of X-rays while rotating the X-ray generator and the X-ray detector relative to the subject. Projection data indicating a degree of X-ray attenuation (degree of X-ray absorption by the subject) are collected for each rotational angle during the CT imaging, and a tomographic image (CT image) of the subject is formed based on the projection data obtained at a plurality of rotational angles.
During the process of CT imaging, if the imaging target site such as an organ moves due to a body movement of the subject such as the respiratory movement, artifacts or the like may arise in the CT image that is finally obtained. In consideration of this, in the related art, there is proposed a respiration synchronization scan or the like in which the respiratory movement of the subject is detected and the CT imaging (scan) is executed to match a phase which can be assumed to have no movement or the like of the organ due to respiration (refer to Patent Literature 1 and 2).